A device and a method of the aforementioned generic type are known from document WO 2009/043187 A1. This document proposes a method and device for producing knitted fabric, in which a fibre bundle, which has been drawn to the desired fineness in an upstream stretching system, is laid in front of each of the knitting needles of a knitting machine. On the segment between the stretching system and the knitting needles, the fibre bundle is transported by a pneumatically operating spinning nozzle. By means of the spinning nozzle, the fibre bundle is strengthened in such a way that twining fibres entwine a core of the fibre bundle, in which the fibres are substantially twist-free and orientated largely mutually parallel. In this context, the core of the fibre bundle comprises the greatest proportion of the fibres with respect to the cross-section thereof. The twining fibres entwine the core, and overlap and snag on one another. The resulting strengthening of the fibre bundle is not equivalent to effective yarn twisting, such as can be achieved for example on ring spinning frames. Instead, the spinning nozzle merely forms what is known as a false strand, the twist of which would more or less release if the fibre bundle entwined with twining fibres subsequently had to pass over longer transport segments onto the spinning nozzle on the way to the knitting machine.
Therefore, in document WO 2009/043187 A1, a tube, through which the entwined fibre is provided directly to the knitting needles of the knitting machine on a short path, is used directly after the spinning nozzle. By means of the knitting needles, the fibre bundle subsequently undergoes definitive strengthening within the produced knitting fabric. The known method has the advantage that it can achieve a particularly soft feel of the produced knitted fabric by using a fibre bundle which is merely peripherally strengthened.
However, it is disadvantageous that in document WO 2009/043187 A1 it is always necessary to position the knitting needles of the knitting machine as close as possible to the spinning nozzle. Although technically speaking this is in principle possible, it is not expedient in practice. Accordingly, the technology disclosed in document WO 2009/043187 A1, with which it is not possible to achieve sufficient strength of the fibre bundle for conventional further processing of the fibre bundle, has not been successful in practice.
Document DE 10 2006 037 714 A1 discloses a device for producing a knitted fabric, in which each knitting position of the knitting device is upstream from a stretching unit for producing a drawn fibre bundle. In this context, at least one active transport element for the drawn fibre bundle is arranged between the output roller pair of the stretching unit and the knitting position. The active transport element may consist of a supply unit, which is formed for example of a pair of rollers. In this context, one or more twisting devices, depending on the distance, are arranged between the output roller pair of the stretching unit and the active transport element, and give the fibre bundle, which basically consists of parallel fibres, sufficient strength for transport to the knitting position. Spinning tubes, each comprising a pneumatically operating twisting nozzle, are proposed as twisting devices. If the distance between the active transport element and the knitting position is smaller than the average fibre length of the drawn fibre bundle, the fibre bundle can be supplied to the knitting position directly. However, if this distance is larger than the average fibre length, another, further twisting device is arranged between the active transport element and the knitting position, and gives the drawn fibre bundle sufficient strength for the transport.
Further, document WO 2007/093166 A2 discloses a circular knitting machine for producing a knitted fabric from fibrous material, in which stretching units are assigned to the stitch formation positions of the circular knitting machine. In this context, it is proposed to equip the stretching units with straps, which are formed longer than is conventional in the transport direction of the stretching unit and to which a gripping device is assigned, which is axially displaceable in the transport direction and which produces an additional gripping zone in the primary drawing zone of the stretching unit in the gap formed by the straps. As a result, the conventional degree of gripping can be adapted to the length of the fibres used, so as to improve the uniformity of the fibrous materials exiting the stretching unit.
Document DE 10 2007 052 190 A1 includes a method and a device for improving the quality of a fibre bundle made of staple fibres leaving a stretching unit. In this context, it is proposed to arrange a sensor, for the fibre band or roving entering the stretching unit, upstream from the stretching unit. As a result, the quality of the fibre bundle or process upstream from the stretching unit can be monitored and weak points can be eliminated there. Moreover, if mass fluctuations of the fibre bundle or roving are detected, the stretching unit or a downstream stretching device can be stopped.